OK, I loaded up plugger, as I mentioned before. Then I saw that it insisted on loading PDF documents in the browser window, something I don't like at all. No problem, right? Just edit the /etc/pluggerrc-5.0 file, commenting out the application/pdf and text/pdf lines.
Except that didn't work with MozillaFirebird. No matter how many times I restarted it, cleared the cache, etc., when I did about:plugins I saw that plugger still wanted to handle PDF files.
After some scratching my head, I looked in the .phoenix directory, where I found a file pluginreg.dat with yesterday's date on it. That file said the plugger would handle the PDF files. You think this file would be rewritten every time Firebird starts up, but that's apparently not the case. So I deleted the file, restarted Firebird, and, lo and behold, plugger no longer worries about PDF files.
Does this happen in Mozilla? Netscape? Is it a bug, or a feature? Have to do some looking around to find out.